Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating. In industry, both hot water and water heated to steam have many uses.

The gallon is a measure of volume approximately equal to four litres. Historically it has had many different definitions, but there are three definitions in current use. In United States customary units there are the liquid (? 3.79 L) and the lesser used dry (? 4.4 L) gallons.

The Scots gallon was a Scottish unit of measurement of liquids that was in use from at least 1661, (possibly 15th century), until the mid 19th century. It was approximately three times larger than an Imperial gallon that was adopted in 1824.

A unit of volume for liquid measure equal to four quarts, in particular

80 PLUS is an initiative to promote more energy efficient computer power supply units (PSU). It certifies products that have more than 80% energy efficiency at 20%, 50% and 100% of rated load, and a power factor of 0.9 or greater at 100% load.

eighty: being ten more than seventy

Solar hot water retrofit - before

Solar hot water system installed in 1988. Hot water heater (propane, 40 gallons) in the foreground, and solar holding tank (blue, 80 gallons) in the background. The solar holding tank holds hot water from the solar collectors on the house roof.

Solar Water Heater

This solar water heater is incorporated into the general design of the building and provides 80 gallons of hot water without the use of electricity or gas.